In a conventional disposable diaper, it sometimes occurs that a discharged body liquid migrates through the interior of a topsheet under the effect of capillary action and reaches a peripheral edge portion with a result of leakage therefrom. As a technique for preventing the leak of a liquid from the opposite side edge portions in the longitudinal direction of the diaper, Japanese Patent Application Laid-open No. 63-182401 proposes a diaper in which a sheet material for forming an upstanding gather and a topsheet are joined together at an upper part of an absorbent core and the leak of a body liquid from opposite side edge portions of the diaper is restrained by utilizing the joined section (or junction).
However, since the topsheet of this diaper is designed such that its end portion does not reach an end portion of the product and joining means for joining the upstanding gather serves as leak restraining means, the processing conditions for joining a plurality of sheets are limited. Moreover, in the case where an adhesive agent is used as means for joining the upstanding gather and the topsheet together, in the case where the topsheet is a bulky nonwoven fabric, a large amount of adhesive agent must be used for the adhesion thereof and for the restraint of leak thereof, thus resulting in problems of impairment of flexibility and increase in manufacturing cost. Moreover, in the case where a continuous production is to be performed, the topsheet must be arranged intermittently in a direction of the flow of a raw fabric, thus resulting in serious deterioration in productivity. In addition, the anti-leak effect is not sufficient, as well.